This is much more realistic and can find more issues. This causes the
"mixed cluster" tests to be run twice so I had to fix the tests to work
in that case. In most cases I did as little as possible to get them
working but in a few cases I went a little beyond that to make them
easier for me to debug while getting them to work. My test changes:

1. Remove the "basic indexing" tests and replace them with a copy of the
tests used in the OSS. We have no way of sharing code between these two
projects so for now I copy.
2. Skip the a few tests in the "one third" upgraded scenario:
  * creating a scroll to be reused when the cluster is fully upgraded
  * creating some ml data to be used when the cluster is fully ugpraded
3. Drop many "assert yellow and that the cluster has two nodes"
assertions. These assertions duplicate those made by the wait condition
and they fail now that we have three nodes.
4. Switch many "assert green and that the cluster has two nodes" to 3
nodes. These assertions are unique from the wait condition and, while
I imagine they aren't required in all cases, now is not the time to
find that out. Thus, I made them work.
5. Rework the index audit trail test so it is more obvious that it is
the same test expecting different numbers based on the shape of the
cluster. The conditions for which number are expected are fairly
complex because the index audit trail is shut down until the template
for it is upgraded and the template is upgraded when a master node is
elected that has the new version of the software.
6. Add some more information to debug the index audit trail test because
it helped me figure out what was going on.

I also dropped the `waitCondition` from the `rolling-upgrade-basic`
tests because it wasn't needed.

Closes elastic#25336